Subsea Dispersant Injection (SSDI) - Summary Findings from a Multi-Year Research and Development Industry Initiative

Abstract

ABSTRACTNew and novel results regarding effectiveness and use of subsea dispersant injection (SSDI) are presented in this paper. These findings are relevant for operational guidance, decision making and improvement of models of subsea releases of oil and gas. More specifically, the paper presents data from a comprehensive set of laboratory experiments to measure the initial formation of oil droplets and gas bubbles from a subsea blowout with and without SSDI.Many subsea blowout scenarios for oil and gas will form relatively large oil droplets (multiple millimeters) which rise rapidly through the water column to possibly form thick slicks on the ocean surface, potentially very near the source. On the other hand, smaller oil droplets (< 500 microns) rise more slowly and can stay suspended in the water column for days to weeks.Our laboratory studies examined the influence of different variables on the initial oil droplet size including oil release velocity, dispersant dosage, dispersant injection method, oil temperature, pressure, gas-to-oil ratio, oil type, and dispersant type. Results revealed that dispersant injection is highly effective at reducing droplet size. SSDI has, for this reason, a potential to reduce floating oil and associated volatile hydrocarbons that may threaten worker health and safety. Reduced surfacing may also reduce the amount of oil that reaches ecologically sensitive shoreline environments. Oil that disperses into the water column, as small droplets, may cause temporarily elevated exposure to marine organisms, but these droplets rapidly dilute and later naturally degrade. Dispersed oil dilutes in three dimensions rather than only the two dimensions available for surface oil, and mostly one dimension available to shoreline oil.Our data fit a modified Weber scaling algorithm that predicts initial oil droplet size for both laboratory and field scales. Predictions indicate that SSDI can reduce oil droplet sizes by an order of magnitude for field scales like those experienced in the Deep Water Horizon.In summary, this paper shows that SSDI applied to a subsea blowout is a highly efficient oil spill response tool that, under the appropriate conditions, can substantially delay oil surfacing, reduce the amount of surfacing and reduce the persistence of surface slicks by reducing oil droplet size. The net result is enhanced worker safety and health as well as reduced oil impacts on the surface and shoreline.